晶體管特性文獻(xiàn)翻譯綜述

1、晶體管特性第一章中已經(jīng)指出，晶體管能夠放大電流。因此，晶體管在電子線路中應(yīng)用很廣， 例如音頻放大器，助聽(tīng)器，擴(kuò)音機(jī)放大器，無(wú)線電接收機(jī)和電視接收機(jī)，測(cè)量?jī)x表和工 業(yè)控制。另外，晶體管也可以用作“電子開(kāi)關(guān)”，它可使電流通路或者呈現(xiàn)高電阻或者 呈現(xiàn)低電阻。這就是晶體管有可能在計(jì)算機(jī)電路和控制系統(tǒng)中獲得廣泛應(yīng)用。對(duì)每一項(xiàng)應(yīng)用都必須進(jìn)行細(xì)致的電路設(shè)計(jì)，在能夠系統(tǒng)地進(jìn)行設(shè)計(jì)工作之前，應(yīng)對(duì) 晶體管這一電路元件的特性有個(gè)詳盡的了解，知道什么是最佳工作電壓和電流，對(duì)信號(hào) 的阻抗有多大，晶體管的放大倍數(shù)有多大，什么是晶體管輸出端內(nèi)阻抗等等。這些特性 資料可從各類晶體管有關(guān)數(shù)據(jù)中獲得，這些數(shù)據(jù)由制造廠商提供，印成

2、“數(shù)據(jù)表”發(fā)行, 使晶體管使用者能根據(jù)此進(jìn)行初步設(shè)計(jì)，而不必自行量測(cè)。首要的問(wèn)題是取得晶體管電壓電流關(guān)系曲線。通常要提供出兩組曲線；發(fā)射結(jié)正向 電壓電流特性曲線，通常稱為發(fā)射極特性曲線或輸入特性曲線；以及集電結(jié)反向電壓電 流曲線，通常稱為集電極特性曲線或輸出特性曲線。1基特性曲線首先研究共基極電路，圖1所示為發(fā)射極基極正向特性曲線，它描述了發(fā)射極電流 如何隨發(fā)射極基極電壓從零正向增高而增大。 圖上所示的特性曲線是小型鍺管的典型曲 線。由圖可看出，最初電流隨電壓增高而增加，但增加的幅度很小。在這期間，外加電 壓逐漸克服pn結(jié)的勢(shì)壘。勢(shì)壘一旦被中和，電流就迅速增加。發(fā)射極電流皿現(xiàn)在來(lái)研究發(fā)射極電流

3、變化時(shí)集電極電路出現(xiàn)的情況。首先，發(fā)射極電流為零時(shí)集 電極基極特性如圖2中Ie=O的曲線所示它和前面圖所示的pn結(jié)反向特性曲線相似。圖中的小股電流稱為集電結(jié)的漏電流。 現(xiàn)在使發(fā)射結(jié)電流增加到1毫安（圖1中的A點(diǎn)），并使之維持不變。我們看到，幾乎 全部發(fā)射極電流都傳送到集電極，通過(guò)集電極的電流量與集電極電壓的高低無(wú)關(guān)。這樣,集電極電壓電流特性曲線就成了圖 2中Ie=2, 3,4和5毫安時(shí)的集電極曲線B,C, D和E。 集電極特性曲線幾乎處于水平位置這一性質(zhì)突出了高輸出電阻這一特性，因而集電極電壓發(fā)生大幅度變化時(shí)，電流變化很小。集電極電壓A* 1ET嚴(yán)匚iE=3D)iE=4ED-1-2-3-4圖2

4、集電極基極特性由圖中可以看出，甚至在集電極電壓為零時(shí)仍然存在集電極電流。這是因?yàn)榛鶚O電 流在通過(guò)基區(qū)電阻時(shí)在集電極基極回路中產(chǎn)生一小電勢(shì)差，從而在集電極兩端形成很小的反向偏壓。要使集電極電流減為零，就需要外加一很小的正向集電極電壓，如圖2所示。圖2中集電極特性曲線畫在第三象限，以使人們注意到集電極反向偏置?，F(xiàn)在一般 把它畫在第一象限，如圖3所示，這在某種程度上是由于熱離子管的輸出特性曲線本身 就是這樣處理的。護(hù)Ie=2Ie j7IE=0010集電極電壓 V20>&(»&圖3集電極特性曲線2共基極放大器的相位關(guān)系基極發(fā)射極回路是正向偏置。以pnp晶體管為例，它的發(fā)

5、射極與基極相比為正。信 號(hào)正向半周與Vee串聯(lián)連接時(shí)，發(fā)射極比以前更正，使發(fā)射極基極電流增大。在晶體管中，發(fā)射極基極電流的增大使集電極電流相應(yīng)增加。由于Rl中的電流方向朝上，此電阻器上端與它的下端相比較就比以前更正了。因此，正向半周輸入信號(hào)引 出正向半周輸出信號(hào)。這就是說(shuō)共基極晶體管放大器沒(méi)有倒相問(wèn)題。護(hù).-滬P輸廠亠宀 輸出電R>«¥eemmVcc圖4 共基極放大器的倒位關(guān)系在許多類型的多級(jí)放大器、振蕩器和電視用視頻放大器中，相位關(guān)系是考慮的重要問(wèn)題。對(duì)今后的應(yīng)用來(lái)說(shuō)，重要的是要記住我們?nèi)绾闻袛嗟瓜嗯c否的方法。3單電源共基極電路N-P-NRL圖5單電池共基極電路共基

6、極電路的設(shè)計(jì)通常避免使用發(fā)射極電池Vee。要做到這一點(diǎn)，只需加上一基極電阻（Rb）,并使此電阻的低端成為輸入和輸出回路兩者的公共端。此電路除了省去發(fā) 射極電池外，還使一個(gè)輸入端和一個(gè)輸出端處于低電位。這樣，輸入和輸出兩個(gè)回路現(xiàn) 在都有一個(gè)公共的參考電位（低電位）。流過(guò)Rb的小股電流Ico和地連接，它相對(duì)于基 極是負(fù)的（這是npn晶體管）。因而不用電池就獲得了較小的正向偏壓。偏置電阻Rb可 以旁路，這樣在可能出現(xiàn)交流信號(hào)時(shí) Rb的電壓降仍保持不變。4共發(fā)射極特性曲線共發(fā)射極連接時(shí)可得出與共基極連接時(shí)相類似的特性曲線。首先是輸入特性曲線，它表明基極電流隨發(fā)射極基極結(jié)兩端電壓正向升高而變化的情況，如

7、圖6所示；其次是輸出特性曲線，它表明集電極電流隨不同基極電流下的集電極電壓變化已定 的情況下，基極電流變化比發(fā)射極電流變化小。圖 7的輸出特性曲線和共基極特性曲線 很相似，只是電流曲線有明顯的坡度，即電流隨電壓而增大。這說(shuō)明它的輸出電阻比基 極電路低，但它仍然是相當(dāng)高的。此外，集電極電壓為零時(shí)集電極電流也為零，這是因 為基極電流所形成的電勢(shì)并沒(méi)有出現(xiàn)在集電極反射極回路。/L7一一00. 05 山 1 0. 15 丄 2 C. 25基極電圧 V圖6共發(fā)射極特性曲線50005000502 2 1 1-r嚴(yán)A 廠 4： n , !尸Lr1150 Llf® 1 u g 口 : Ak.iBOr

8、iA嚴(yán)1il i山LIco05101520集電極電壓V圖72N78輸出特性曲線5集電極曲線的應(yīng)用當(dāng)你觀察集電極曲線時(shí)，首先映入眼中使你感興趣的是電流并不隨集電極電壓的變化而急劇增大。它是一組十分近似于水平的直線，特別在基極電流很低的區(qū)域；即使在 基極電流較高的區(qū)域，坡度也很平緩的。我們可以說(shuō)：在制造廠商所推薦的區(qū)域范圍內(nèi), 晶體管的集電極電流相對(duì)獨(dú)立于集電極電壓。nVc =廠5V/60 1)0150213D 250 3 D070集電根電涼圖8 lb Ic曲線5 4 3 2與之相反，在集電極電勢(shì)恒定的條件下，基極電流稍有變化就可使用集電極電流發(fā) 生較大的變化。基極電流作等值增長(zhǎng)時(shí)，集電極電流是否

9、相應(yīng)地等值上升呢？為了弄清這一點(diǎn)，我們選定一集電極電勢(shì)，譬如說(shuō) 5伏，然后沿這條5伏線上升。注意觀察基極電流每增加25毫安時(shí)集電極電流的變化情況。為幫助你估算集電極電流的變化量，我 們繪制了集電極電勢(shì)為5伏的lb Ic曲線。雖然這條曲線并不完全是一條直線，但它確實(shí)很近似于直線，如果晶體管用于例如 音頻放大電路，我們就可以說(shuō)：如果lb的變化局限在相當(dāng)小的范圍內(nèi)，集電極電流就隨 lb作線性變化。這一提法可進(jìn)一步解釋如下：如饋入基極的輸入電流是弱音頻電流，則集電極回路 的電流變化比輸入電流的變化大，但其波形保持不變。這樣，我們得到一種度量我們對(duì) 這類晶體管所能要求的保真度的方法，或者反過(guò)來(lái)說(shuō)，度量晶

10、體管固有畸變的方法。無(wú)畸變輸入傳輸輸出畸變輸入輸出傳輸圖9晶體管畸變曲線只要lb Ic曲線是條直線，其固有畸變就為零。曲線的曲率越大，晶體管本身所造成的畸變?cè)絿?yán)重前面所有討論的前提是，電路元件選擇恰當(dāng)，才能使所用的晶體管產(chǎn)生正常的偏壓 不然，就可能出現(xiàn)與晶體管固有特性無(wú)關(guān)的畸變。集電極電壓圖10 Ic的改變影響lb的改變我們可利用集電極特性曲線或者lb Ic曲線在幾秒鐘內(nèi)即可估算出晶體管的 B值。 晶體管集電極特性一般可在制造廠商的參數(shù)表中取得。讓我們利用它來(lái)校核晶體管 2N78的？值，即常說(shuō)的所謂的基極電流增益。晶體管2N78通常在5伏集電極電位下工作，我們先找出 5伏線，然后沿此線選出 基

11、極電流變化的一般區(qū)域范圍內(nèi)，例如從 100微安到125微安。利用我們已經(jīng)知道的等 式B = Ic/ lb,取lb從100微安到125微安的變化為 lb，它等于25微安。然后，我 們可注意到在lb的變換范圍內(nèi)lc從2.9毫安變?yōu)?.5毫安。將這些值代入等式就得到：_3.5-2.9 卩=0.0250.6= 0.025=246單電池共發(fā)射極電路關(guān)于這個(gè)電路，讓我們先回顧第三節(jié)雙電池共基極放大器改成單電池電路的部分。 你可能會(huì)發(fā)現(xiàn)，為了提供所需要的偏置電位，需要在基極回路上外加一電阻和電容。電 阻R.使基極相對(duì)于發(fā)射極（正向偏置）和集電極（反向偏置）都具有正確的極性。如果我們進(jìn)一步分析雙電池共基極電路

12、，顯然可知，需要外加偏壓元件的原因在于 發(fā)發(fā)射極和集電極電流的流動(dòng)方向。我們用pnp晶體管為例，可知le和lc在接向基極的 公共引線中流動(dòng)方向相反。由于用一個(gè)電池，不論放在電路的哪個(gè)部分，要在一個(gè)元件 中產(chǎn)生兩股方向相反的電流是決不可能的，所以為了建立正常的偏置電位，借助于人為 的輔助元件即偏置電阻是完全必要的。信描圖11雙電池共發(fā)射極電路現(xiàn)在我們來(lái)分析雙電池共發(fā)射極電路。vee使電子流向通過(guò)Ri（或通過(guò)信號(hào)源本身，假設(shè)信號(hào)源是連續(xù)直流的）和基極到發(fā)射極，再向下經(jīng)過(guò)公共導(dǎo)線回到電池的正端，女口 深色箭頭所示。Vee使電子流向通過(guò)FL和集電極到發(fā)射極，再向下經(jīng)過(guò)公共連接線回到 電池的正端，如淺色

13、箭頭所示。由此可知，從發(fā)射極到兩組電池正極結(jié)點(diǎn)的公共導(dǎo)線中電流的流向相同。這就很容 易用一組電池來(lái)完成原來(lái)兩組電池的工作。不管我們把電池接到那里，一定要記住，pnp 晶體管的基極相對(duì)于發(fā)射極應(yīng)是負(fù)的，但負(fù)的程度不如集電極。Vpr Vcc圖12發(fā)射極和集電極電流的流動(dòng)同向圖13單電池基極發(fā)射極放大電路實(shí)際上去掉第二組電池很容易，這不能不使我們感到奇怪，為什么在共發(fā)射極電路 中曾經(jīng)使用過(guò)兩組電池。我們只注意到 Vee和Vcc相對(duì)于發(fā)射極都是負(fù)的。全面檢查線 路的連接，我們很快就可看出，集電極電流的通路與過(guò)去完全相同；從電池的負(fù)端通過(guò) 集電極，離開(kāi)發(fā)射極，又回到正端。與此同時(shí)，同一電池按深色箭頭指示

14、的方向把電流 （雖然可能很?。┧腿牖鶚O回路。 這股電流的流動(dòng)和采用兩組電池時(shí)的情況完全相同。剩下要作的只是選擇適當(dāng)?shù)碾娮?值，使基極電壓大小合適。由于Ri阻值大小在很大程度上取決于晶體管類型、Vcc的電勢(shì)和環(huán)境溫度，所以我們無(wú)法提供某一定值。晶體管2N78在標(biāo)準(zhǔn)中頻電路室溫下的Ri典型阻值為10,000歐姆左右。來(lái)自晶體管原理附：英文原文Transistor CharacteristicsIt has been shown in the previous chapter that the transistor is cable of amplifying electric currents.

15、As a result, it can be used for many applications in electronic circuits, such as audio amplifiers, hearing aids, pubic address amplifiers, radio and television receivers, in strume ntati on and in dustrial con trol. Also, the tran sistor can be used as an "electro nic switch ", that is it

16、 can prese nt either a high or a low resista nee to the passage of curre nt. This ope ns up the possibility of wide use in computer circuits and control systems.For each application careful circuit design work must be carried out. Before this can be done systematically, it is necessary to have detai

17、led knowledge of the characteristics of the characteristics of the transistor as a circuit element, that is, to know what is the best operating voltage and current, what impedance is presented to the signal, what amplification the transistor will give, what is the internal impedance of the transisto

18、r at the output, and so on.Data from which in formatio n of this n ature can be obta ined is prepared by the manu facturerdata shtbetsse”caHoon each type of tran sistor and published as prelim inary desig n without hav ing to make measureme nts himself.First, it is importa nt to derive groups of vol

19、tage-curre nt relati on ships for the tran sistor.Two sets of curves are no rmally prese nted, the forward voltage-curre nt characteristics of the emitter junction, referred to as the emitter characteristics curves of the collector junction, called the collector characteristics or the output charact

20、eristics.1 Common Base CharacteristicsCon sideri ng first the com mon base arran geme nt, Fig. 1 shows the emitter to base forward characteristic, that is, how the emitter curre nt in creaser as the emitter to base voltage is in creased positively from zero. The characteristic show n is typical of a

21、 small germa nium tran sistor. It will be see n that at first the curre nt in creases only very slightly as the voltage is increased.During this region the applied voltage is overcoming the potential barrier of the junction. Once the barrier has bee n n eutralized, the curre nt in creases rapidly.4a

22、. 2EMITTER-BASE VOLTAGE, VOLTSFig 1 Input charactcrijric of commonba?c circuit.Now consider what happens in the collector circuit when the emitter current is varied. At first, with zero emitter curre nt, the collector to base characteristic is show n as the cure for in Fig. 2. This is similar to the

23、 reverse characteristic of a pn junction shown previously in Fig The small current is known as the leakage current of the collector junction. Now let the emitter curre nt be in creased to 1 mA point A in Fig. 1 and held con sta nt at that value. We have seen that nearly all of the emitter current pa

24、sses to the collector, the amount of current crossing the collector junction not being dependent on the collector voltage. Thus thecollector voltage current characteristic will now be curve A for E=1 in Fig. 2.IE=nAJrE= iE0Ci嚴(yán)D)EiE=sCOLLECTOR VOLTAGE VOLTS -5-4-3-2-1Fig 2 Collector charateristic, co

25、mmon base circuit.Similarly, as the emitter curre nt is in creased in further steps collector curves B,C,D and E are obtained for emitter current Ie=2,3,4 and 5 mA. The almost horizontal nature of the collector characteristics emphasizes the high output resista nee, a large cha nge of collector volt

26、age produc ing only a very small cha nge of curre nt.It will be seen that the collector current is maintained even at zero collector voltage. Thisis because the base curre nt, i n flow ing out through the resista nee of the base regi on, sets up a small pote ntial which appears in the collector-base

27、 circuit, and con stitutes a small reverse bias across the collector junction. To reduce the collector curre nt to zero it is n ecessary to apply a small forward collector voltage as shown in Fig. 2.4rIE=JfrfioaaCOLLECTOR VOLATAGE, VOLTSFig? Collctor charatenstic, coimnonbase circuitHMHaME Ho-L3mooO

28、UTPUTFig4 There ts noifiYetsion ina coititnoti-base tiamsistor ainplifieiIn Fig. 2 the collector characteristics have bee n show n in the third quadra nt as a remin der that the collector jun ctio n is biased in the reverse direct ion. It is now customary to prese nt them in the first quadra nt as s

29、how n in Fig. 3, to some exte nt because the output characteristics of thermio nic valves were always draw n in this way.2 Hase Relations in a Common-Base AmplifierF-ST-FINPUT._. The base-emitter circuit is forward-biased. In the case of the pnp transistor used as an example, this means that the emi

30、tter is more positive tha n the base. Whe n a positive-go ing half-cycle is now inserted in series with V ee ,the emitter becomes more positive than before, in creas ing the emitter-base curre nt. In a tran sistor, an in crease of emitter-base curre nt produces a corresp onding in crease of collecto

31、r curre nt. Since the direct ion of curre nt flow is upward in Rl, the top terminal of this resistor must become more positive than it was before with respect to the bottom termi nal. Hence a positive-go ing in put half-cycle gives rise to a positive-go ing output half-cycle. This means that there i

32、s no phase inv ersi on in the com mon base tran sistor amplifier.Phase relations are important considerations in many types of multistage amplifiers. In oscillators, and in video amplifiers for television. It is important to remember how we determ ine whether phase inv ersi on does or does not occur

33、 for future use.3 Single-battery Common-base CircuitVrrFigj The cottirtion-base circuitA com mon-base circuit is no rmally desig ned to do away with the n eed for an emitter battery Vee To do this we n eed merely add a base resistor(R and make the lower term inal of this resistor com mon to both in

34、put and output circuits. In additi on to doing away with the emitter battery, this circuit makes it possible to maintain one in put and one output term inal at ground pote ntial . There is now a com mon refere nee pote ntial(gro und) for both in put and output. The small leakage current Ico flowing

35、through R b places the base at a slightly higher positive pote ntial tha n ground. Since the emitter is conn ected to ground through Re, this element must be negative with respect to the base(this is an npn transistor). Thus, the small amount of for-ward-bias is obtained without the need for a batte

36、ry. The bias resistor Rb may be bypassed to maintain the voltage drop across it constant, despite the possible presence of alter nat ing sig nal curre nts.4 Common Emitter CharacteristicsWith the com mon emitter connection, similar characteristics can be prepared. First, the in put characteristic, w

37、hich shows how the base curre nt varies as the voltage across the emitter-base jun cti on is in creased in the forward direct ion, as show n in Fig. 7. It will be see n from Fig. 6 that the in put resista nee is higher tha n for the com mon base arran geme nt, the cha nge of base curre nt being smal

38、ler tha n the cha nge of emitter curre nt for a give n cha nge of emitter to base voltage .The output characteristics in Fig. 7 are similar to the com mon base characteristics except that there is now a noticeable slope on the current lines, the current in creas ing with voltage. This in dicates tha

39、t the output resista nce is lower tha n in the com mon base arrangement; but nevertheless it is still high. Also, the collector current is now zero for zero collector voltage since the pote ntial produced by the base curre nt does not appear in the collector to emitter circuit.BASE VOLATAGE, VOLTSFi

40、gg Iput characteristic of common emitter ciicuitCOLLECTOR VOLATAGE, YOLTSF1E7 Collctar charat eristic, conunon 亡rtiittM circuit5 Using the Collector CurvesOne of the first in terest ing things that strikes you as you look at the collector curves is that the current does not rise very rapidly with ch

41、angesof collector voltage. Notice how horiz on tai the graph lines are, especially whe n the base curre nt is low. Eve n for higher base curre nts, the slopes are very shallow. We can say it this way: over the range recomme nded by the manufacturer, the collector current of a transistor is relativel

42、y independent of the collector voltage.On the other hand, a small change of base current always produces a relatively large cha nge in collector curre nt, if the collector pote ntial is maintained con sta nt. Does the collector curre nt rise in equal steps for equal in creme nts of base curre nt? To

43、 see this, choose a certa in collector potential, say 5 volts, then follow the 5-volt line upward and note how the current cha nges, we have draw nb Ic curve for a collector pote ntial of 5 volts.Vc 二5V/E54a SD IDO 15D 也口 25n 3DQBASE CUTTENT8 Ib-Ic curve for 2N7S transistor with Vc at 5 volts.Althou

44、gh this curve is not a perfect straight line, it certainly does approach it closely. Of the transistor is used in an audio amplifier circuit, for example, we might then say: If the range of variati on of Ib is held within reas on ably small limits, the collector curre nt varies lin early with it.Thi

45、s may be in terpreted as follows: if the in put curre nt to the base is a weak audio current, the current variations in the collector circuit will be large but will have the same waveform. Thus, we arrive at a measure of the fidelity or, conv ersely, the in here nt distortio n that we may expect fro

46、m a transistor of this type. As long as the b Ic curve is a straight line, the in here nt distortio n will be zero. The greater the curvature of the graph, the greater will be the distortion that can be attributed to the transistor itself.NO DISTORTIONINPUTDISTORTIONINPUTkamsistorOUTPUTtramsistorOUT

47、PUTFig 9 氏 curved iiamsistor charatensticmay introduce distrotionAll of the foregoing presupposesthat the circuit components have been selected to produce the proper bias for the specific tran sistor used. If this is not the case, distorti on may occur that has no conn ecti on with the in here nt ch

48、aracteristics of the tran sistor.COLLECTOR VOLATAGE, VOLTSFig 10 A small part of the Collctor charatensticEither the collector characteristic curves or the lbIc curve may be used to estimate the beta of a tran sistor in just a few sec on ds. Since the collector characteristics are those gen erally f

49、ound in manu facturers' rati ng sheets, suppose we use these to check the beta, or base curre nt gain as it is ofte n called, of the 2N78.Since this transistor normally operates at a collector potential of 5 volts, we first locate the 5-volt line. Then we select an average regi on of base curre

50、nt cha nge along this line, say from 100 microamperes to 125 microamperes. Using our kno wledge that beta = Ic/ Ib ,we can take the change of Ib from 100 卩 A to 125 卩 A for a total of Ib=25 卩 A . We then note that I c goes from 2.9 ma to 3.5 ma over this range of I b .Substituting these values in th

51、e equati on we have:3.5-2.90.6=24P 0.0250.0256 The Single-Battery Common-Emitter CircuitAt this poin t, let us refer back to where we con verted the two-battery com mon-base amplifier into a single-battery circuit. You will find that it was necessaryto add a special resistance and capacitor in the b

52、ase circuit to provide the required biasing potentials. That is, Rbpermits the base to have the correct polarity with respect to the emitter(forward bias)and with respect to the collector (reverse bias).If we an alyze the two-battery com mon-base circuit further, it is appare nt that the reas on for

53、 the need of an extra biasing component lies in the directions of flow of the emitter and collector currents. Using a pnp transistor as an example (the npn is analyzed the same way except that all curre nt direct ions are reversed), we see thae and Ic flow in opposite direct ions in the com mon lead

54、 going to the base. Since one battery, placed any where at all in the circuit, could n ever produce two oppositely-directed curre nts in a com mon eleme nt, it is n ecessary to create the correct bias potentials by means of an artificial aid the bias resistor.Now let us an alyze the two-battery com mon-emitter circuit. Vee forces curre nt up through Ri (or through the signal source itself if the source has d-c continuity), through the base to the emitter, the n dow nward through the com mon lead back to the positive termi nal of the battery as shown by the d